The invention relates generally to a method for handling snapshots together with migrated files in a managed storage management, and more specifically, handling snapshots together with migrated files in a managed storage. The invention relates further to a related system for handling snapshots together with migrated files in a storage management system, and a computer program product.
Enterprise IT (information technology) management continues to struggle with the management of vast amounts of data. The problem has been addressed by classifying the data with respect to their availability for access in different time categories. Instantly required data may be stored in the main memory of a computer system, data required in milliseconds may be stored on disk storage systems and data not required immediately may be swapped out to, e.g., tape storage systems or other longer-term storage systems. Storage systems having such tiered storage architecture—e.g., disk system as a first-tier storage (also tier-1 storage) and a long-term storage as a second-tier storage (also tier-2 storage)—may be denoted as hierarchical storage management (HSM) systems. Such HSM may represent a compromise between the data access time and the cost of storing large amounts of slowly changing or less critical data.
On the other side, snapshots may be generated from active systems, i.e., from data being stored in the first-tier storage. Typically, such multi-tier storage environments may be accessed using a standardized access method like DMAPI (data management application user interface). However, there exist incompatibilities between HSM functions and snapshots of the life data, i.e., data in the first-tier storage.
For a user, it may be completely transparent in an HSM system were a file may be stored—the first-tier storage or the second-tier storage. Typically, a stub file may be created in the file system if the original file is moved from the active storage system—i.e., from the first-tier storage—to the second-tier storage. For the user, a stub file cannot be distinguished from the original file because all metadata are shown—e.g., in a file explorer—as if it would be the original file, e.g., the file size. The file size may be shown as, e.g., 10 MB for a video file, although the related stub file may only require a couple of hundred bytes.
For traditional HSM managed storage systems the conflict between the migrated files and snapshot become visible: If the user wants to free space in the first-tier storage, he may delete one or more files in the first-tier storage. However, if the file was an HSM migrated file—i.e., only the stub file exists in the active, first-tier storage—the user may only delete a couple of hundred bytes. But at the same time, the original file with a couple of MBs needs to be brought back from the second-tier storage to the snapshot. Thus, the problem turns out to be: if the user deletes a file that is part of a snapshot, in the first-tier storage, the original file is brought back from the second-tier storage if there is at least one snapshot of the file. This may increase the amount of storage required for storing data in the first-tier storage. Hence, the opposite of the objective—reducing the amount of data stored in the first-tier storage—is achieved without intention. This may represent the conflict between HSM migrated files and snapshots.